1. Field of the Invention
The present invention relates to a particle therapy system, and more particularly to a particle therapy system suitable for accelerating an ion beam, such as a proton or heavy ion beam, by an accelerator to be used in medical treatment.
2. Description of the Related Art
A particle therapy system employing an ion beam, such as a proton or heavy ion beam (hereinafter referred to also simply as a “beam”), for treatment of cancers is designed to be able to irradiate the beam in match with the shape of a diseased part in the body of a patient so that the beam is concentrated to the diseased part. In particular, adjustment of the beam range in the direction of depth from the body surface of the patient can be realized by adjusting energy of the beam.
A typical example of accelerators used in the particle therapy system is a synchrotron. The synchrotron has an RF cavity for acceleration (hereinafter referred to as an “RF cavity”) in which an RF voltage is applied to an orbiting beam and the beam is accelerated to a desired level of energy. The beam having been accelerated to the desired level of energy is extracted from the synchrotron, is introduced to an irradiation apparatus through a beam transportation line, and is irradiated to the diseased part (cancer) in the body of the patient lying on a treatment couch.
The irradiation apparatus produces a beam in match with the size of the cancer and the depth thereof from the body surface of the patient, and then irradiates the produced beam. In general, the irradiation apparatus is constructed to be able to irradiate the beam based on one of known beam irradiation methods, i.e., a double scattering method (p. 2081 and FIG. 35 of Non-Patent Reference 1; “REVIEW OF SCIENTIFIC INSTRUMENTS”, Vol. 64, No. 8 (August 1993), pp. 2079-2093), a wobbling method (p. 2084 and FIG. 41 of Non-Patent Reference 1), and an ion beam scanning method (Patent Reference 1; JP,A 10-118240 and pp. 2092-2093 of Non-Patent Reference 1).
Regardless of which one of those beam irradiation methods is utilized, the synchrotron constituting the accelerator of the particle therapy system is required to control energy of the extracted beam to a set energy level with high accuracy. To that end, the beam energy requires to be measured with high accuracy. It has hitherto been known to measure the beam energy by employing a water phantom disclosed in Patent Reference 2; JP,A 11-64530 and a multi-leaf Faraday cup described in Non-Patent Reference 2; “BEAM COMMISSIONING OF THE NEW PROTON THERAPY SYSTEM FOR UNIVERSITY OF TSUKUBA”, M. Umezawa, et al., Proceedings of 2001 Particle Accelerator Conference, Chicago, USA (2001)).